Over the years we have been spotted by our feathered friends a lot. Some seem to have no effect while others tend to fade the canvas slightly. I am pretty sure it won't have any great effect on the canvas, so don't stress about it.
When you can get up and about then open up the camper and remove the poo then. Don't scrub at it with a hard bristle brush (like I did to a tent years ago as it WILL take the colour out of the canvas), but get a very wet cloth and leave it sitting on the affected area to loosen up the now rock hard excrement, then wipe off. If it has faded slightly underneath then wear it as a badge of honour because it shows you are using your camper at least.
You are right with your first thought and that is to get it off as quickly as possible, certainly at the pack up stage. Just be thankful that it not a present left by bats, now that is fun.